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September 9, 2003 A. Cardini / INFN Cagliari 1
M. Alfonsi1, G. Bencivenni1, W. Bonivento2, A.Cardini2,
C. Deplano2, P. de Simone1, F. Murtas1, D. Pinci3,
M. Poli-Lener1, D. Raspino2, B. Saitta2
Aging Test at Aging Test at CasacciaCasaccia
1. Laboratori Nazionali di Frascati - INFN, Frascati , Italy
2. Sezione INFN di Cagliari – Cagliari, Italy
3. Sezione INFN di Roma 1, Roma, Italy
September 9, 2003 A. Cardini / INFN Cagliari 2
Aging at Casaccia-1
PC
60CoB
OTTLES
HV
CONTROLROOM
4.5
m
Casaccia
GEMA,B,D
P
GEM-CGEM-E
Ar/CO2/CF4 = 45/15/40, 200 cc/min
Module 0.1 (chambers A e B) + chamber D (10x10 cm2) @ 16 Gray/h
Chamber C (old 20x24 cm2) as a monitor @ 0.5 Gray/h
Chamber E (very old 20x24 cm2) equipped with ASDQ (96 ch.) @ 0.1-0.2 Gray/h HV(“reference”) = 1280 V, G ~ 6x103;
Monitor H2O, T e P: ± 1ppm, ± 0.1°K, ± 0.1mb (Panametrics/MKS)
September 9, 2003 A. Cardini / INFN Cagliari 3
exhaust
MKSmixerAr
CO2CF4
C
B
A
D
E
CO 60
not in scale
T, RH probePatm probe
Polypropilene-gas pipes
Stainless steel-gas pipes
Gas mixture supply & P,T,RH monitoring
September 9, 2003 A. Cardini / INFN Cagliari 4
tp
TtV
norm eiti
0
We used the knowledge ofdependenceof the gain on
V(t)*T(t)/P(t)
to correct and normalized the detector current
T (
oK
)P (
mb)
T/P
(oK
mb
-1)
Time (days)
Temperature and Pressure in the gas mixture
September 9, 2003 A. Cardini / INFN Cagliari 5
Results from Casaccia-1
Current decrease rate seems proportionalto gas water content
Below a few water ppm currents seems not to vary too much
No changes in current for the monitor chamber (“C”) in the whole period
Norm
aliz
ed C
ur r
ent s
( A
)W
ate
r (p
pm
)
Time (days)
A
B
H20
11.4 LHCb years
8.5 LHCb years
itot/i -67 %
itot/i -60 %
2 C/cm2
1.5 C/cm2
September 9, 2003 A. Cardini / INFN Cagliari 6
Aging Mechanism ?Even if we are not yet completely sure (surface chemical analysis is currently in progress) we believe that the current decrease is related to the etching of the copper on the GEM foils due to hydrofluoric acid (HF).
HF is produced in the reaction F- + H20 HF + OH-, and this could explain the large current decrease rate when water content in the gas mixture is above 10 ppm.
It should be noted however that local aging tests we performed in the past, both with X-rays (~ 1cm2, 10 LHCb year with G/G < 5%) and at PSI (hadronic beam @ 300 MHz per at least 5 days on ~15 cm2, for a total of ~ 5 years at LHCb with NO variations in detector efficiency), did not show such a large gain variations.
We suspect that the reduced gas flow – which could not be increased by 20 as the accelerating factor – could be partially responsible of these high current reductions.
September 9, 2003 A. Cardini / INFN Cagliari 7
Aging Mechanism ?New GEM foil Aged GEM foil
Copper etched away close to the GEM hole ?
50 m
September 9, 2003 A. Cardini / INFN Cagliari 8
To check if the current reduction rate depends on the gas mixture water content we built 2 new 10x10 cm2 detectors
These detectors were dried in an oven at 50 ºC and then exposed to gammas in Casaccia at 16 Gray/h for a week
The Casaccia-1 large detectors (A and B) and the monitor chamber (C) were irradiated as well
To control the gas contamination possibly generated by radiation we supplied the gas to the two new detectors with an independent gas line
We did not start the aging test until the gas water content was below 0.5 ppmV
The Casaccia-2 Aging Test
September 9, 2003 A. Cardini / INFN Cagliari 9
T, P and H2O
Always below 0.5 ppmV !
Temp.
Press.
T/P
H2O
(T/P) -1.6% !
September 9, 2003 A. Cardini / INFN Cagliari 10
A
B
Raw (no T/P correction) currents
0.35 C/cm2 ~ 2 LHCb y
0.13 C/cm2 ~ 0.75 LHCb y
September 9, 2003 A. Cardini / INFN Cagliari 11
C
new Dnew E
Raw (no T/P correction) currents
itot/i -10 %(Only due to T/P variations)
0.45 C/cm2 ~ 2.6 LHCb y
0.35 C/cm2 ~ 2.0 LHCb y
Voltage change
September 9, 2003 A. Cardini / INFN Cagliari 12
A
B
Normalized currents
0.35 C/cm2 ~ 2 LHCb y
itot/i -20 %
itot/i -8 %
0.13 C/cm2 ~ 0.75 LHCb y
September 9, 2003 A. Cardini / INFN Cagliari 13
Normalized currents
0.45 C/cm2 ~ 2.6 LHCb y
0.35 C/cm2 ~ 2.0 LHCb y itot/i -20 %
itot/i -35 %
Very Preliminary
new D new E
September 9, 2003 A. Cardini / INFN Cagliari 14
• It seems that there is a small effect due to the water content of the gas mixture, but this is important only at very high radiation rates.
• It also seems that there is a dependence of the current reduction rate on the gas flow. This is suggested by the local aging tests (X-rays and PSI).
• For these reasons we believe that the Casaccia test is much more destructive than a non-accelerated test. This is also suggested by the behavior of the monitoring chamber, where we do not see any gain reduction in 1 LHCb equivalent year, while we clearly see for example a –8% current reduction in 0.75 LHCb years for chamber B at Casaccia-2.
Preliminary conclusions on aging
September 9, 2003 A. Cardini / INFN Cagliari 15
Gas flows during various tests
Aging Test Gas (cc/min)
Current (uA) Current/flow
Standard 100 ~ 0.01-0.05 ~ 0
X-rays 100 0.2 0.4 .002 .004
PSI 200 ~ 50 0.25
Casaccia big 350 800 1000 2.3 2.9
Casaccia small
200 100 150 0.5 0.75
Casaccia mon.
350 60 0.17
Sauli (Hamburg)
80 3 12 0.04 0.15
M1R1 estimation
~ 100 (?) 12 ~ 0.12 (?)
September 9, 2003 A. Cardini / INFN Cagliari 16
What’s next?
• Chemical surface analysis on GEM foils
• Local gain measurement on aged detectors
• Efficiency measurement on aged detectors
• X-rays detector aging at various gas flows
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